The present invention relates to a color image display device that displays a color image with one light valve as a light modulating member. Also, the present invention relates to a projection-type image display apparatus including such a color image display device.
A liquid crystal projector now part of the mainstream in the market of large-screen displays uses a light source lamp, a focusing lens and a projection lens to magnify and form an image of a liquid crystal panel (a light valve) onto a screen. Currently commercialized systems can be classified roughly into a three-plate system and a single-plate system.
In the former system of the three-plate liquid crystal projector, after a light beam from a white light source is separated into light beams of three primary colors of red, green and blue by a color separation optical system, these light beams are modulated by three monochrome liquid crystal panels so as to form images of the three primary colors. Thereafter, these images are combined by a color combination optical system so as to be projected onto a screen by one projection lens. Since the entire spectrum of the white light from the light source can be utilized, this system has a high efficiency of light utilization. However, because of the necessity of the three liquid crystal panels, the color separation optical system, the color combination optical system and a convergence adjusting mechanism between the liquid crystal panels, this system is relatively expensive.
On the other hand, a conventional single-plate system liquid crystal projector is compact and inexpensive because an image formed on a liquid crystal panel having a mosaic color filter simply is magnified and projected onto a screen. However, since this system obtains light with a desired color by absorbing light with an unwanted color out of white light from the light source by using the color filter as a color selection member, only one-third or less of the white light that has entered the liquid crystal panel is transmitted (or reflected). Accordingly, the efficiency of light utilization is low and high-brightness images cannot be obtained easily. When the light source is brightened, the brightness of the displayed image can be improved. However, there remain problems of heat generation and light resistance owing to light absorption by the color filter, making it very difficult to increase the brightness.
In recent years, as a way to eliminate light loss owing to the color filter in this single-plate system, a new configuration in which the efficiency of light utilization is raised by using dichroic mirrors and a microlens array instead of the color filter has been suggested and also commercialized.
A conventional single-plate projection-type image display apparatus, which improves the efficiency of light utilization using the dichroic mirrors and the microlens array, will now be described. FIG. 30 shows a schematic configuration thereof, and FIG. 31 shows a detailed cross-section of a light valve of the projection-type image display apparatus shown in FIG. 30.
A projection-type image display apparatus 900 has a light source portion 901, an illuminating device 903, a color separation optical system 907, a transmission-type light valve 902 and a projection lens 908. A white light beam from the light source portion 901 irradiates an effective region of the light valve 902 by means of the illuminating device 903. The color separation optical system 907 includes a red-reflecting dichroic mirror 904, a green-reflecting dichroic mirror 905 and a total reflection mirror 906 that are arranged obliquely. The white light beam that has passed through the illuminating device 903 enters the color separation optical system 907, thereby being separated horizontally into three light beams of primary colors of red, green and blue, so as to enter the light valve 902. The transmission-type light valve 902 has pixels that can modulate the incident light beams of the respective colors independently by an input signal corresponding to each of the red, green and blue light beams, with these pixels being arranged horizontally in one element.
The white light beam emitted from the light source portion 901 is led to the color separation optical system 907 by the illuminating device 903. A red light beam in the incident light is reflected by the red-reflecting dichroic mirror 904 placed obliquely with respect to the incident light so as to travel along an optical axis 909. A green light beam in the light transmitted by the red-reflecting dichroic mirror 904 is reflected by the green-reflecting dichroic mirror 905 placed obliquely with respect to the incident light so as to travel along an optical axis 910. A blue light beam transmitted by the green-reflecting dichroic mirror 905 enters the reflection mirror 906, and is then reflected so as to travel along an optical axis 911. The red light beam on the optical axis 909, the green light beam on the optical axis 910 and the blue light beam on the optical axis 911 pass through a condenser lens 912 and reach the transmission-type light valve 902.
As shown in FIG. 31, an entrance-side polarizing plate 913 is provided as a polarizer on the side of an entrance surface of the transmission-type light valve 902, and only the light beam having a predetermined polarization direction in the incident light is transmitted by this polarizing plate 913. The transmitted light enters a microlens array 918 including a group of microlenses 917 with their longitudinal direction being in a vertical direction. The horizontal width of the microlens 917 corresponds to the total horizontal widths of a pixel aperture for red 914, a pixel aperture for green 915 and a pixel aperture for blue 916. The red light beam that has traveled along the optical axis 909 and entered the microlens 917 obliquely at an incident angle of xcex81 is focused on the pixel aperture for red 914. The green light beam that has traveled along the optical axis 910 and whose chief ray entered the microlens 917 at a right angle is focused on the pixel aperture for green 915. The blue light beam that has traveled along the optical axis 911 and entered the microlens 917 obliquely from the direction opposite to the red light at an incident angle of xcex81 is focused on the pixel aperture for blue 916. The light beam of each color that has passed through the pixel aperture for each color enters an exit-side polarizing plate 919 provided on an exit surface of the transmission-type light valve 902. The exit-side polarizing plate 919 has a polarization axis arranged orthogonal to the polarization axis of the entrance-side polarizing plate 913. Since a light beam that has entered a pixel aperture to be displayed as white is emitted with its polarization direction being rotated by about 90xc2x0 in a liquid crystal layer, it is transmitted by the exit-side polarizing plate 919 and reaches the projection lens 908. Since a light beam that has entered a pixel aperture to be displayed as black is emitted without being subjected to the rotation of its polarization direction in the liquid crystal layer, it is absorbed by the exit-side polarizing plate 919 and does not reach the projection lens 908. The transmission-type light valve 902 rotates the polarization direction of the incident light at every pixel so as to display an image.
In the single-plate projection-type image display apparatus with the new configuration in which the efficiency of light utilization is raised as described above, it is possible to achieve a high efficiency of light utilization close to that in the three-plate system without wasting the light from the light source.
However, in this configuration, a bright lens whose f-number is smaller than 1/(2 sin (xcex82+xcex83)) is required as the projection lens 908, where a half-angle of a cone of rays converging from the microlens 917 toward the pixel aperture is expressed by xcex82 and an incident angle at which the chief ray of the red light or the blue light enters the pixel aperture is expressed by xcex83 (An actual f-number is 1.0 to 1.5).
Accordingly, even when the single-plate system is adopted so as to use one display device, the size and the cost of the projection lens increase in practice. Thus, its advantage over the three-plate system is not readily apparent.
Furthermore, since a light beam of each color from the light source is led to the pixel of a corresponding color, the resolution of an image display panel (the transmission-type light valve 902) has to be three times as high as a necessary resolution in order to achieve high resolution. This increases the cost of the image display panel, and also lowers transmittance when the transmission-type light valve is used as the image display panel. Moreover, when the resolution of the image display panel is low, or when an image is magnified considerably, colors of red, green and blue appear separately, causing image quality deterioration such as convergence dislocation.
In response to the above problems, an image display apparatus is suggested in JP 4(1992)-316296 A. FIG. 32 shows a schematic configuration of this image display apparatus.
A white light beam emitted from a light source portion 920 is led to a color separation optical system 921. As shown in FIG. 33, the color separation optical system 921 includes dichroic mirrors 921a and 921b and two reflection mirrors 921c and 921d. The dichroic mirror 921a reflects blue light and transmits green light and red light. The dichroic mirror 921b reflects red light and transmits green light and blue light. These dichroic mirrors 921a and 921b are crossed. A blue light beam 932 out of a white light beam 931 from the light source portion 920 is reflected by the dichroic mirror 921a, reflected by the reflection mirror 921d and passes through an aperture 922b of an illumination portion 922. A red light beam 933 is reflected by the dichroic mirror 921b, reflected by the reflection mirror 921c and passes through an aperture 922r of the illumination portion 922. A green light beam 934 is transmitted by both the dichroic mirrors 921a and 921b and passes through an aperture 922g of the illumination portion 922. The apertures 922r, 922g and 922b of the illumination portion 922 are formed like a belt (a rectangle), and the light beams of red, green and blue are emitted adjacent to each other from these apertures.
The belt-like light beams of respective colors emitted from the illumination portion 922 pass through a scanning optical system 924, and then illuminate different regions of a single transmission-type light valve (a display panel) 923 in a belt-like manner. With an effect of a rotating prism 924a constituting the scanning optical system 924, the belt-like light beams of red, green and blue scan the light valve 923 from the bottom to the top. When a belt-like illuminated region of one of the light beams goes beyond the uppermost end of an effective region of the light valve 923, the belt-like illuminated region of this light beam appears at the lowermost end of the effective region of the light valve 923 again. In this manner, the light beams of red, green and blue can scan continuously over the entire effective region of the light valve 923. A light beam illuminating each row on the light valve 923 varies moment by moment, and a light valve driving device (not shown in this figure) drives each pixel by an information signal according to the color of the light beam that is illuminated. This means that each row of the light valve 923 is driven three times at every field of a video signal to be displayed. A driving signal inputted to each row is a color signal corresponding to the light beam illuminating this row among signals of the image to be displayed. The light beams of these colors that have been modulated by the light valve 923 are magnified and projected onto a screen (not shown in this figure) by a projection lens 925.
With the above configuration, the light beam from the white light source is separated into light beams of three primary colors, so that the light from the light source can be used with substantially no loss and the efficiency of light utilization can be increased. Also, since each of the pixels on the light valve displays red, green and blue sequentially, the color dislocation, which has been a problem in the three-plate system mentioned above, is not caused, making it possible to provide a high quality image.
However, in the above configuration, the light beams of these colors from the illumination portion 922 are not focused when transmitted by the rotating prism 924a. Since the size (the radius of gyration) of the rotating prism 924a has to be in accordance with a region illuminated by the light beam emitted from the illumination portion 922, the rotating prism 924a becomes large and heavy. This has made it difficult to reduce the size and weight of the apparatus.
Furthermore, a powerful motor for rotating the rotating prism 924a becomes necessary, causing an increase in the size and cost of the apparatus.
It is an object of the present invention to solve the above-described problems of the conventional image display apparatus and to provide a color image display device that is provided with a scanning optical system for scanning an illuminated portion (a light valve) sequentially with light beams of individual colors, thus achieving a high efficiency of light utilization, a reasonable price and a miniaturization of the apparatus.
In order to achieve the above-mentioned object, the present invention has the following configurations.
A first color image display device of the present invention includes a light source portion for emitting respective light beams of red, green and blue, a first optical system that the respective light beams from the light source portion enter, a rotating polygon mirror that the respective light beams having left the first optical system enter and that makes the respective light beams perform a scanning while reflecting the respective light beams, a second optical system for leading the respective light beams from the rotating polygon mirror to an illumination position, an image display panel that is arranged at the illumination position and provided with a plurality of pixels for modulating an incident light according to a color signal of red, green or blue, and an image display panel driving circuit for driving each of the pixels of the image display panel by a signal corresponding to a color of light entering this pixel. Belt-like regions illuminated by the respective light beams are formed substantially in parallel with each other on the image display panel and moved continuously by the scanning, thereby displaying a color image. Chief rays of the respective light beams enter a reflecting surface of the rotating polygon mirror so as not to overlap each other and at different angles from each other with respect to a rotation direction of the rotating polygon mirror. The chief rays of the respective light beams that have been reflected by the rotating polygon mirror enter the second optical system at different angles from each other and then enter different positions of the image display panel.
A second color image display device of the present invention includes a light source portion for emitting respective light beams of red, green and blue, a first optical system that the respective light beams from the light source portion enter, three rotating polygon mirrors that the respective light beams having left the first optical system respectively enter and that make the respective light beams perform a scanning while reflecting the respective light beams, a second optical system for leading the respective light beams from the rotating polygon mirrors to an illumination position, an image display panel that is arranged at the illumination position and provided with a plurality of pixels for modulating an incident light according to a color signal of red, green or blue, and an image display panel driving circuit for driving each of the pixels of the image display panel by a signal corresponding to a color of light entering this pixel. Belt-like regions illuminated by the respective light beams are formed substantially in parallel with each other on the image display panel and moved continuously by the scanning, thereby displaying a color image. The three rotating polygon mirrors are formed as one piece so as to match their rotation axes and have their phases in a rotation direction shifted from each other. Chief rays of the respective light beams that respectively have been reflected by the three rotating polygon mirrors enter the second optical system at different angles from each other and then enter different positions of the image display panel.
A third color image display device of the present invention includes a light source portion for emitting respective light beams of red, green and blue, a first optical system that the respective light beams from the light source portion enter, three rotating polygon mirrors that the respective light beams having left the first optical system respectively enter and that make the respective light beams perform a scanning while reflecting the respective light beams, a second optical system for leading the respective light beams from the rotating polygon mirrors to an illumination position, an image display panel that is arranged at the illumination position and provided with a plurality of pixels for modulating an incident light according to a color signal of red, green or blue, and an image display panel driving circuit for driving each of the pixels of the image display panel by a signal corresponding to a color of light entering this pixel. Belt-like regions illuminated by the respective light beams are formed substantially in parallel with each other on the image display panel and moved continuously by the scanning, thereby displaying a color image. The three rotating polygon mirrors respectively are rotated about rotation axes different from each other. Chief rays of the respective light beams that respectively have been reflected by the three rotating polygon mirrors enter the second optical system at different angles from each other and then enter different positions of the image display panel.
According to the first to third color image display devices described above, it becomes possible to display a color image by using a light valve that is not provided with pixels exclusively for the respective colors, without using a color filter. Thus, an image can be displayed with a high efficiency of light utilization and a high resolution. Furthermore, by providing a scanning optical system using the rotating polygon mirror, a small and low-cost image display device can be provided.
In the first to third color image display devices described above, it is preferable that the second optical system is an optical system in which a height of the light beams at the illumination position changes in proportion to an incident angle of the light beams. This makes it possible to move (scan) the illuminated regions on the image display panel easily.
In the first to third color image display devices described above, it is preferable that, when an angle at a rotation axis subtended by one reflecting surface of the rotating polygon mirror is expressed by xcex8P (xcex8P=2xcfx80/n, where n is the number of the reflecting surfaces provided in the rotating polygon mirror), the light beams that have entered the second optical system at an incident angle xcex8P are focused at a position in which a height of the light beams is greatest in the scanning direction on the image display panel. This can raise the efficiency of light utilization.
Also, in the above-described first color image display device, it is preferable that, when the chief rays of the respective light beams entering the rotating polygon mirror respectively are called a first chief ray, a second chief ray and a third chief ray in an order of the rotation direction of the rotating polygon mirror, an angle at the rotation axis subtended by a line segment from an incident position of the first chief ray into the reflecting surface of the rotating polygon mirror to that of the second chief ray into the reflecting surface of the rotating polygon mirror and an angle at the rotation axis subtended by a line segment from the incident position of the second chief ray into the reflecting surface of the rotating polygon mirror to that of the third chief ray into the reflecting surface of the rotating polygon mirror are both about xcex8P/3. Accordingly, the chief rays of the respective colors meet a border of the reflecting surfaces of the rotating polygon mirror at an even time interval, allowing an image displayed with enhanced color uniformity and brightness uniformity and reduced flicker.
Furthermore, in the above-described first color image display device, it is preferable that, when an angle that the first chief ray forms with the second chief ray is expressed by xcex8C1 and an angle that the second chief ray forms with the third chief ray is expressed by xcex8C2, the following relationship is satisfied.
(xcex8C1+xcex8C2)xc3x973/2xe2x89xa62xc3x97xcex8P
This makes it possible to use light from the light source portion for the illumination of the image display panel without wasting it.
Moreover, it is preferable that the angle xcex8C1, and the angle xcex8C2 are both about 2xc3x97xcex8P/3.
Next, a fourth color image display device of the present invention includes a light source portion for emitting respective light beams of red, green and blue, a first optical system that the respective light beams from the light source portion enter, a rotating polygon mirror that the respective light beams having left the first optical system enter and that makes the respective light beams perform a scanning while reflecting the respective light beams, a second optical system for leading the respective light beams from the rotating polygon mirror to an illumination position, an image display panel that is arranged at the illumination position and provided with a plurality of pixels for modulating an incident light according to a color signal of red, green or blue, and an image display panel driving circuit for driving each of the pixels of the image display panel by a signal corresponding to a color of light entering this pixel. Belt-like regions illuminated by the respective light beams are formed substantially in parallel with each other on the image display panel and moved continuously by the scanning, thereby displaying a color image. An area of each of the belt-like regions illuminated by the respective light beams is substantially equivalent to one-third of an effective region of the image display panel. The second optical system is an optical system in which a height of the light beams at the illumination position changes in proportion to an incident angle of the light beams. When an angle at a rotation axis subtended by one reflecting surface of the rotating polygon mirror is expressed by xcex8P (xcex8P=2xcfx80/n, where n is the number of the reflecting surfaces provided in the rotating polygon mirror), the light beams that have entered the second optical system at an incident angle xcex8P are focused at a position in which the height of the light beams is greatest in the scanning direction on the image display panel. When chief rays of the respective light beams entering the rotating polygon mirror respectively are called a first chief ray, a second chief ray and a third chief ray in an order of the rotation direction of the rotating polygon mirror, an angle at the rotation axis subtended by a line segment from an incident position of the first chief ray into the reflecting surface of the rotating polygon mirror to that of the second chief ray into the reflecting surface of the rotating polygon mirror and an angle at the rotation axis subtended by a line segment from the incident position of the second chief ray into the reflecting surface of the rotating polygon mirror to that of the third chief ray into the reflecting surface of the rotating polygon mirror are both about xcex8P/3. When an angle that the first chief ray forms with the second chief ray is expressed by xcex8C1 and an angle that the second chief ray forms with the third chief ray is expressed by xcex8C2, the angle xcex8C1 and the angle xcex8C2 are both about 2xc3x97xcex8P/3.
According to the fourth color image display device described above, it becomes possible to display a color image by using a light valve that is not provided with pixels exclusively for the respective colors, without using a color filter. Thus, an image can be displayed with a high efficiency of light utilization and a high resolution. Furthermore, by providing a scanning optical system using the rotating polygon mirror, a small and low-cost image display device can be provided.
In the first to fourth color image display devices described above, the light source portion may include a light source for emitting a white light beam including red, green and blue light beams and a color separation optical system for separating the white light beam into the red, green and blue light beams. By using the white light source and obtaining the red, green and blue light beams with the color separation optical system, it is possible to raise the efficiency of utilization of light from the light source.
In this case, it is preferable that an optical distance from an incident portion to an emitting portion in the color separation optical system is substantially the same for each color of the light beams. This can reduce the difference in size of the spots of the respective light beams that are formed on the reflecting surface of the rotating polygon mirror, thereby maintaining a focusing efficiency for each of the light beams at a high level.
Also, in the first to fourth color image display devices described above, it is preferable that the second optical system includes an fxcex8 lens. This makes it possible to move (scan) the illuminated regions on the image display panel easily.
Furthermore, in the first to fourth color image display devices described above, the image display panel may be a transmission-type light valve. Alternatively, the image display panel may be a reflection-type light valve.
Moreover, in the first to fourth color image display devices described above, it is preferable that an illuminating f-number in the scanning direction is smaller than that in the direction orthogonal thereto in optical systems from the first optical system to the image display panel. The illuminating f-number in the scanning direction is made relatively smaller, thereby preventing the outline in the scanning direction of the illuminated regions from becoming vague on the image display panel so as to deteriorate color purity. In addition, the illuminating f-number in the direction orthogonal to the scanning direction is made relatively larger, thereby allowing the miniaturization of the apparatus.
Also, in the first to fourth color image display devices described above, it is preferable that the first optical system is provided with a stop having a rectangular aperture. This makes it possible to form spots with substantially uniform sizes on the reflecting surface of the rotating polygon mirror even when the length of optical path is different for each of the light beams.
Furthermore, in the first to fourth color image display devices described above, it is preferable that the light source portion includes an integrator optical system. This can secure the uniformity of illumination in the direction orthogonal to the scanning direction of the image display panel.
The above-mentioned integrator optical system can be configured such that the integrator optical system includes a first lens array and a second lens array, with the first lens array being a group of microlenses having identically-shaped rectangular apertures, and the second lens array being a group of microlenses corresponding to the microlenses of the first lens array on a one-to-one basis. The first optical system includes a first lens and a second lens. Incident light beams into the microlenses of the first lens array are focused on the corresponding microlenses of the second lens array, aperture shapes of the microlenses of the first lens array are superimposed on the first lens, and images of the aperture shapes of the microlenses of the first lens array that have been superimposed on the first lens are formed on the image display panel via the second optical system, thus forming the belt-like illuminated regions.
It is preferable that the first lens forms an image of the second lens array on the reflecting surface of the rotating polygon mirror via the second lens. This can reduce the size of the reflecting surface, allowing the miniaturization of the rotating polygon mirror, thus contributing to the miniaturization of the entire apparatus.
Also, it is preferable that an overall shape of the group of the microlenses of the second lens array is formed such that its image, when being formed on the reflecting surface of the rotating polygon mirror, has a dimension in a direction corresponding to the rotation direction smaller than that in a direction orthogonal thereto. This can reduce the dimension of the reflecting surface in the rotation direction, allowing the miniaturization of the rotating polygon mirror, thus contributing to the miniaturization of the entire apparatus.
It also is preferable that the first lens array includes a plurality of microlenses that are formed to have different centers of curvature with respect to an aperture center, so that the incident light beams into the microlenses of the first lens array are focused on the corresponding microlenses of the second lens array. This makes it possible to design the arrangement of the microlenses of the second lens array freely, so that the shape of the image to be formed on the reflecting surface of the rotating polygon mirror described above can be optimized, for example.
In addition, it is preferable that each size of apertures of the microlenses of the second lens array is designed according to a size of the corresponding images formed by the first lens array. This can minimize the size of the second lens array, while preventing a reduction in the efficiency of light utilization.
It is preferable that the light source portion further includes a light source for emitting a white light beam including red, green and blue light beams and a color separation optical system for separating the white light beam into the red, green and blue light beams, and the integrator optical system is provided between the light source and the color separation optical system. By using the white light source and obtaining the red, green and blue light beams with the color separation optical system, it is possible to raise the efficiency of utilization of light from the light source. In addition, even when using a discharge tube as the light source, it is possible to secure the uniformity of illumination in the direction orthogonal to the scanning direction of the image display panel.
In this case, it is preferable that an optical distance from an incident portion to an emitting portion in the color separation optical system is substantially the same for each color of the light beams. This can reduce the difference in size of the spots of the respective light beams that are formed on the reflecting surface of the rotating polygon mirror, thereby maintaining a focusing efficiency for each of the light beams at a high level.
In addition, a projection-type image display apparatus of the present invention includes any of the first to fourth color image display devices and a projection optical system for magnifying and projecting an image formed on the image display panel. Since any of the first to fourth color image display devices of the present invention is used, an image can be displayed with a high efficiency of light utilization and a high resolution, and a small and low-cost projection-type image display apparatus can be provided.